1. Field of the Invention
The invention relates to an optical collimator structure and, particularly, to an optical collimator structure using an optical fiber provided with a plurality of cores.
2. Description of the Related Art
In the field of optical communication, various optical circuit modules, for operations such as combination and branching of signal lights, and for switching optical paths, are used. An optical collimator structure is provided with configuration for emitting a parallel flux of light from an optical fiber or receiving a parallel flux of light. Optical collimator structures include, in addition to those making signal light into parallel flux of light using a single core optical fiber, those having collimator structures using two core optical fibers, as shown in FIG. 5 (see, for example, Japanese Unexamined Patent Publications (Kokai) No. 9-230169 (JP 9-230169 A) and Japanese Unexamined Patent Publications (Kokai) No. 2002-267876 (JP 2002-267876 A).
In FIG. 5, a first optical fiber for an inlet port is indicated by reference numeral 10a, and a second optical fiber for an outlet port is indicated by 10b. The cores of the first and second optical fibers 10a, 10b, which are exposed by removing the respective claddings, are indicated by reference numerals 12a, 12b. A capillary 14 accurately aligns the optical axes of the cores 12a and 12b with each other and supports them. The capillary 14 is made of a ceramic, such as zirconia. The cores 12a, 12b are aligned with each other by inserting them in holes penetrating the capillary 14. The capillary 14 and the optical fibers 10a, 10b are supported by a ferrule 16. Specifically, the capillary 14 is supported by pressing it into the ferrule 16, and the optical fibers 10a, 10b are supported by adhering them, to the fixing opening in the ferrule 16, with an adhesive 18.
An optical lens 20 is positioned in front of the ferrule 16. The optical lens 20 serves as a collimator that receives an incident beam of light from the core 12a of the first optical fiber 10a and emits a parallel beam of light toward a mirror 22, and receives a parallel beam of light from the mirror 22 and emits a beam of light so as to collect it to the end face of the core 12b of the second optical fiber 10b. 
Thus, in the optical collimator structure of FIG. 5, the mirror 22 is positioned, in front of the optical lens 20, to reflect the parallel beam of light emitted from the optical lens 20, and collect the reflected beam of light to the end face of the core 12b through the optical lens 20. This optical collimator structure represents an example comprising a dual-core optical fiber assembly 10, which has two optical fibers 10a, 10b each having the core 12a, 12b, and uses the first optical fiber 10a as an inlet port, and the second optical fiber 10b as an outlet port.
As shown in FIG. 5, a conventional optical collimator structure constructed using a multi-core optical fiber assembly comprising a plurality of unitary optical fibers, in which a unitary optical fiber is employed as an inlet port, and another unitary optical fiber is employed as an outlet port, combines an optical lens 20 with an optical fiber assembly 10. As the optical lens 20, a spherical lens, aspherical lens, SELFOC lens or the like is used. The optical lens 20 is accurately aligned with the optical fiber assembly 10 to provide a collimator structure. In the structure shown in FIG. 5, the optical lens 20 is fixed at the front end of a sleeve 24, and the sleeve 24 is then fixed to the outer periphery of the ferrule 16 by YAG welding while aligning the optical lens 20 with the end face of the cores 12a, 12b supported by the capillary 14 to retain a certain distance therebetween.
In this way, as the conventional optical collimator structure comprising the optical fiber assembly 10 having a plurality of cores uses the optical lens 20 for the construction of the structure, the optical lens 20 must be adjusted with high accuracy, of the order of 1 micrometer, relative to the cores 12a, 12b of the optical fiber assembly 10, which requires a high degree of assembling accuracy. Further, for the fabrication of the conventional optical collimator structure, processing, such as YAG welding of the sleeve 24 to the ferrule 16, is needed, resulting in problems, such as expensive processing and fabrication. In addition, the conventional optical structure has a large number of parts, such as the optical lens 20 and the sleeve 24, which causes a difficulty in reducing the manufacturing cost.